Field of the Invention
The present invention relates to an image pickup apparatus of which the display start timing and the display quality are selectable.
Description of the Related Art
As an image sensor mounted on an image pickup apparatus such as a digital camera, stacked image sensors in which a semiconductor integrated circuit chip (an image pickup chip) having an image pickup unit is stacked on a semiconductor integrated circuit chip (a processing chip) for performing image processing on an image signal, have appeared in recent years. In an image pickup apparatus including such an image sensor, a light that entered an image pickup unit is converted into an electrical signal, and digital image data resulting from an AD conversion of the electrical signal is transferred to a main chip. Then, image processing, display processing, etc. on the image data, are performed on the main chip side. Furthermore, Japanese Laid-Open Patent Publication (kokai) No. 2015-148676 proposes a configuration in which auto-focusing is performed in two stages: on the side of a processing chip in a stacked image sensor and on the side of a main chip, thereby achieving higher precision than that of auto-focusing performed only on the main chip side.
However, recently, the resolution and possible frame rate of an image sensor tend to be increasing significantly, and the amount of data communicated between the image sensor and a main chip is increasing. In general, an image sensor transfers image data obtained by shooting an image to a main chip, and the main chip develops the transferred image data to generate displayable data that can be displayed. In a case where development processing for generating display data is performed on the main chip side in this way, due to the transfer of image data from the image sensor to the main chip and the main chip performing processing such as primary storage of the image data in a memory, it takes time to start the image display. Therefore, the larger the data amount of image data, the longer the delay time to start the image display when the image data is reproduced on a live view. Furthermore, if the communication band between the image sensor and the main chip is insufficient, the transfer takes time, which causes a further delay in the start of the image display. Moreover, the highest speed of development processing in the main chip depends on the data transfer rate; therefore, if the communication band is insufficient, images taken by shooting cannot be reproduced on the live view at the original speed, and end up being reproduced in slow motion.